Many situations exist in which people are near to each other (say within a few hundred yards) and wish to communicate silently and graphically, across the distance that separates them. For example, if two groups of people, each in separate cars, are driving up to the mountains together, one group may wish to draw a map for the other group or suggest a place to stop for lunch. In a classroom or meeting room, individuals may wish to communicate with each other, even when separated by a large table or by several chairs. In amusement parks and shopping malls, parents and children may desire the ability to separate, yet retain the ability to communicate and agree on a later meeting place. In parking lots, airports, auditoriums, or hiking trails, where people often get separated from each other, people would like be to be able to get in touch.
Some techniques for handling these problems exist. When several cars go on a trip together, they can communicate using Citizen's Band (CB) radios. People in classrooms and meetings can pass notes to each other by passing folded pieces of paper from hand to hand. People in large open areas can use walkie-talkies. Motorists in urban centers can also communicate using cellular phones from car to car.
The aforementioned technologies, however, do not permit silent, graphical communication. The noise generated by verbal communication using a walkie-talkie or cellular telephone is inappropriate in a classroom or meeting situation. While a fax machine may provide silent, graphical communication for some applications, this device requires a supply of paper and is not portable.